Gasification apparatuses and methods for generating syngas have been found convenient to convert gasifiable feedstock material into a gaseous fuel by means of a high-temperature process. As a result of rather complex thermo-chemical reactions, gasifiable feedstock, e.g., biomass, is thus transformed into permanent gases such as hydrogen, carbon monoxide, carbon dioxide and methane which usually contain organic vapours which condense under ambient conditions and are known collectively as tar and a solid residue mainly consisting of char and ash.
Conventionally, the gasification process is carried out in a gasifying reactor accommodated in a vessel and the resulting crude permanent gases, in the following called crude syngas, are withdrawn from the vessel and passed through further equipment to remove solid residues as well as to reduce the tar components. The crude syngas contains the above-mentioned permanent gases hydrogen, carbon monoxide, carbon dioxide and methane in varying quantities, depending inter alia on the feedstock material used and on the conditions of the gasification process.
While the solid residues can be removed by a cyclone and eventually a further filtering device, removal of tar components is more difficult. Tar is undesirable because of various problems associated with condensation, formation of tar aerosols and polymerisation to form more complex structures which cause problems in the downstream process equipment as well as the engines and turbines used in applications of the gasification apparatus.
Several tar components condense and/or solidify when the temperature of the syngas drops below about 400° C. Therefore, process equipment which is likely to be affected by tar condensate has to be maintained at temperatures of about 500° C. or more.
Furthermore, the solids removed from the crude syngas and tar still contain gasifiable material.
Various techniques have been proposed in order to recover at least part of the energy contained in the solids removed from the crude syngas and the tar components.
However, such approaches are not satisfying in that still a substantial portion of tar components is contained in the crude syngas removed from the vessel containing the gasifying reactor which creates problems in the following equipment and reduces the yield of syngas. Furthermore, high temperature processing of the crude syngas is required until it has passed the filtering device.
Furthermore, recycling of the solid particulate matter including not yet exhausted, i.e., still gasifiable portions of the feedstock material requires a more complex apparatus and higher maintenance efforts.
The object of the present invention therefore resides in providing an apparatus and a method for generating syngas from gasifiable feedstock material which allows for a higher yield of syngas with reduced costs and efforts.